Ouch!
![Frown :( :(](data:image/gif;base64,R0lGODlhAQABAIAAAAAAAP///yH5BAEAAAAALAAAAAABAAEAAAIBRAA7)
Twine/Sugarcube benefits from years of tweaks to ensure that a game can work well with different browsers and different devices having very different screen sizes and capabilities, to ensure that it is possible to save a game to disk when a browser runs in incognito mode and cannot rely on the local storage, to ensure that the "back" button can work even with saved games, etc. Also, this engine has a strong community support and lots of tools are available to help developers build and debug their games, to help players view and edit their saved games, etc.
Building a new engine from scratch using React is likely to be more difficult than the developer anticipated, and will probably not support many of the features that Twine/Sugarcube supports. I am sure that it is possible to create a very nice-looking user interface with React (been there, done that). But all these other features that Twine/Sugarcube supports about managing the game state and persisting it even in incognito/private mode are not so trivial to implement.